AU637657B2

AU637657B2 - Co-polymer production

Info

Publication number: AU637657B2
Application number: AU67827/90A
Authority: AU
Inventors: David Byrom
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Yield10 Bioscience Inc
Priority date: 1989-12-08
Filing date: 1990-12-07
Publication date: 1993-06-03
Anticipated expiration: 2010-12-07
Also published as: CA2031888C; CA2031888A1; EP0431883B1; US5364778A; EP0431883A3; IN177461B; BR9006231A; EP0431883A2; JPH05236973A; GB9026238D0; ZA909816B; KR910012251A; KR100223341B1; ATE149204T1; DE69029993D1; AU6782790A; GB8927794D0; DE69029993T2; NZ236394A; JP3036851B2

Abstract

A microbiological process, and novel bacteria e.g. Alcaligenes eutrophus NCIMB 40124, for use in such a process. The process enables the more efficient prooduction of copolymers comprising hydroxyvalernate and hydroxybutyrate monomer units.

Description

AUSTRALIA

Patents Act 637657 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art:

S

SApplicant(s): Imperial Chemical Industries PLC Imperial Chemical House, Millbank, London SWlP 3JF, UNITED KINGDOM Address for Service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Complete Specification for the invention entitled: CO-POLYMER PRODUCTION Our

POF

Ref 200346 Code: 1453/1453 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 006 6006 If B 35544 Copolymer production This invention relates to a microbiological method of producing copolymers comprising 3-hydroxybutyrate (HB) monomer units and 3-hydroxyvalerate (HV) monomer units and to a new micro-organism suitably adapted for use in such a microbiological method.

Homopolymer consisting of HB monomer units, known as polyhydroxybutyrate (PHB) is accumulated by various micro-organisms, principally bacteria, as an energy reserve material as granules within the microbial cells.

PHB extracted from such cells is a thermo lastic 0 polyester of the repeat structure S.

-O.CH(CH

3

).CH

2

.CO-

that crystallises to a relatively high level e.g. of the order of 15 70% or more. This crystallisation behaviour is often disadvantageous when the polymer is to be used ao, for example, a moulding material.

It is known that the crystallisation of PHB may be modifiei by incorporation of units of a dissimilar monomer, into 20 the polymer chain and thereby forming a copolymer. Copolymers, comprising HB monomer units and a minor proportion of dissimilar units may be produced by the cultivation of certain micro-organisms, under certain conditions in the presence of certain acids, and alcohols.

Polymers exhibiting an infra-red band said to be indicative of ethylenic unsaturation are described by Davis in "Applied Microbiology" 12 (1964) pages 301 to 304. These polymers which are said by Davis to be copolymers containing 3-hydroxybutyrate units and 3-hydroxy-2-butenoate units, i.e.

units of the formula -O.C(CH3)=CH.COwere prepared by cultivating Nocardia on n-butane.

Wallen et al describe, in "Environmental Science and Technology" 6 (1972) pages 161 to 164 and 8 (1974) pages 576 to 579, a polymer melting at 97 to 100 0 C (after repeated washing) 2 B 35544 isolated from activated sludges and containing 3-hydroxybutyrate units and 3-hydroxyvalerate units, i.e.

-O.CH(C2H 5

).CH

2

.CO-

units in the ratio of Marchessault et al reported in "IUPAC Macro Florence 1980 International Symposium on Macromolecules Preprints" 2 (1980) pages 272 to 275 a study of this polymer and confirmed that it contained mainly 3-hydroxyvalerate units.

United States Patent Specification 3275610 describes the microbiol. ;ical production of polyesters by cultivating certain micro-organisms, especially Nocardia salmonicolor, on carboxylic *o* acids containing 4 carbon atoms.

European Patent Specification 0069497 describes the microbial production of a number of polyesters by cultivating 15 certain micro-organisms especially Alcaligenes eutrophus mutant NCIB 11599 on suitable substrates.

Published European Patent Application 0204442 describes the microbial production of copolymers of HB and HV by the cultivation of Alcaligenes eutrophus mutant NCIB 12080 on primary 20 alcohols having an odd number of carbon atoms, but excluding methanol.

In order to produce copolymers it known to be necessary to provide a substrate, i.e. a source of energy and carbon, comprising a component that is capable of giving rise to the dissimilar monomer units during at least part of the period when copolymer is accumulated. Thus, for example, in order to produce a copolymer, comprising HB monomer units and HV monomer units, the bacteria are required to be cultivated on a substrate comprising a component from which HV is capable of being synthesised, e.g.

propionic acid.

The component that gives rise to the HV monomer units within the copolymer is herein termed the HV component of the substrate.

Specific cultivation conditions are normally needed in order to induce PHE production, and accumulation, in known 3 B 35544 bacteria. Such specific cultivation conditions are also necessary to induce copolymer production, and accumulation.

Some known bacteria produce PHB constitutively, i.e. do not need to be cultivated under specific conditions in order to produce, and accumulate PHB. Nevertheless, unless the aforementioned specific cultivation conditions are employed, even those known strains which produce PHB constitutively may metabolise an HV component such that copolymer is not produced and accumulated.

Furthermore, even when specific cultivation conditions are used, such that copolymer production, and accumulation is induced in known bacteria, only a small proportion of the HV component is converted by the bacteria into HV monomer units.

Thus, the HV component may give rise to non-monomer material, or 15 may be used to synthesise HB monomer units for incorporation into the copolymer, even if the HV component is the sole substrate during the polymer accumulation stage. The metabolism of the HV component, so as to synthesise HB monomer units, may occur to such an extent that significantly less than half of the HV component is 20 converted into the required HV monomer units, and results in the production of copolymers having low percentage levels of HV monomer units.

*In order to ensure that at least some of the HV component is converted into the required HV monomer units, and that the required proportion of HV monomer units are present in *the ccpolymer, the bacteria are required to be provided with a large excess of the HV component.

The low conversion efficiency coupled with the relative high expense of the HV component results in a HB/HV copolymer synthesis route that is expensive.

Furthermore, the necessary presence of such a large excess of the HV component in the substrate presents severe problems with conventional microbial routes for copolymer synthesis in that a potentially toxic environment is generated within which the bacteria are required to be cultivated.

-4- We have found that by identifying a major metabolic pathway, for the conversion of HV component to HB monomer units, and by providing strains of bacteria wherein such a pathway is substantially eliminated, it is possible to devise a process in which copolymers are synthesised at high HV component to HV monomer unit conversion efficiencies.

Accordingly, we provide a microbiological process for the production of copolymers comprising HB and HV monomer units using a PHB accumulating bacterium having substantially no major metabolic pathway for the conversion of HV component to HB monomer units and which is not capable of significant growth when cultivated under otherwise non growth limiting conditions on a substrate consisting essentially of an HV component, which process comprises cultivating the bacterium in an aqueous medium in which the substrate comprises a water soluble assimilable carbon containing HV component and a water soluble assimilable carbon containing HB component, at a desired weight of dry cells per litre of medium under growth limitation conditions conducive to the bacterium synthesising and accumulating copolymer, and thereafter harvesting the copolymer containing bacterium.

We also provide a microbiological process for the production of copolymers comprising HB and HV monomer units using a PHB accumulating bacterium from which a major metabolic pathway for the conversion of HV component to HB monomer units has been substantially eliminated and which is not capable of significant growth when cultivated under otherwise non growth

I

*limiting conditions on a substrate consisting essentially of an 30 HV component, which process comprises cultivating the bacterium in an aqueous medium in which the substrate comprises a water soluble assimilable carbon containing HV component and a water soluble assimilable carbon containing HB component, at a desired weight of dry cells per litre of medium under growth limitation I .o35 conditions conducive to the bacterium synthesising and accumulating copolymer, and thereafter harvesting the copolymer containing bacterium.

"The process conditions under which the bacterium is.

The process conditions under which the bacterium is 4a cultivated, i.e. temperature, pH, aeration, essential nutrients, may be similar to those commonly used in PHB accumulation processes.

Those essential nutrients required for the growth of the bacterium comprise the following elements, which are normally present in readily assimilable form, normally as water soluble salts: nitrogen, phosphorus, sulphur, potassium, sodium, magnesium, calcium, and iron, together with traces of manganese, zinc and copper.

At least part of the cultivation is conducted under growth limitation conditions, i.e. under conditions wherein an essential requirement for growth but not copolymer accumulation is limited. Under such growth limitation conditions the tendency of the bacterium to produce and accumulate PHB homopolymer is avoided, and the production and accumulation of HV containing e.

O* 0 ft .o *o o *ooo• ."30 *o B 35544 polymer is induced. Whilst it may be possible to induce copolymer accumulation by restricting the supply of oxygen to the bacterium, it is preferred to restrict the supply of one or more of the essential nutrients. The most practical elements to limit are nitrogen, phosphorus, or, less preferably, magnesium, sulphur or potassium. The nitrogen may be conveniently supplied in the form of an ammonium salt, whereas the phosphorus may be conveniently supplied as a phosphate.

Where nitrogen limitation is employed, the substrate is preferably nitrogen free and so amide derivatives of the HV componet a less preferred. The amount of assimilable nitrogen required ii about 10 to 15% by weight of the desired weight of cells less the weight of the accumulated copolymer.

S" Similar considerations apply, where phosphorus *15 limitation is employed.

Cultivation of the bacterium is preferably conducted so that the dry weight of the copolymer-containing cells is at least g.1 1 preferably at least 80 g.l 1, and particularly at least 120 g.l 1 *to. 20 The bacterium used is capable of efficiently converting the HV component present in the substrate to HV monomer units.

Specifically the bacterium can convert the HV component to HV monomer units at an efficiency, on a molar basis, of greater than 45%, particularly at least 60%, and especially between 70 and and further advantageously between 80 and V. Preferably, those conditions under which a specific bacterium should be cultivated are those which maximise the efficiency of conversion.

Cultivation of the bacterium preferably comprises a two stage process. In the first stage the bacterium is preferably grown to a certain dry weight per litre, under non-growth limiting conditions on a readily metabolisable substrate, such as a carbohydrate, for example glucose. In the second stage the substrate is at least in part the HV component, and at least one nutrient required for growth is limited, such that the growth 6 B 35544 limiting conditions exist.

The cultivation may be performed as a batch process, such that copolymer accumulation will occur as the amount of the nutrient required for growth but not copolymer accumulation becomes depleted.

Alternatively, the cultivation may be performed as a continuous process, wherein a stream of culture is removed from the vessel, in which the bacterium is being cultivated, on a continuous or semi continuous basis. The stream removed from the vessel contains bacterium cells in a spent aqueous medium. The spent aqueous medium comprises residual quantities of nutrients 6 too and substrate. The flowrate of the stream leaving the vessel corresponds to the rate of addition of fresh aqueous medium to the o ."vessel. The fresh aqueous medium supplied to the vessel contains

V,

15 nutrients and substrate in sufficient amounts to support "accumulation of uopolymer. Preferably the amount of that nutrient, used to limit the growth of the bacterium, which is fed to the vessel is such that little or none of that nutrient is present in the spent aqueous medium removed from the vessel.

9949 Further, it is preferred that the spent aqueous medium is fed to at least one further aerated cultivation stage under batch or C. 9 preferably continuous or semi-continuous operation, wherein additional copolymer accumulation is stimulated by the addition of fresh HV component containing substrate to the spent aqueous medium. The levels of nutrients and substrate may be adjusted in :Q the spent aqueous medium after leaving the first cultivation stage such that optimum operation of the overall process is maintained.

Alternatively, the cultivation of the bacterium may be conducted as a single stage process. In such a process, wherein copolymer accumulation is induced by limiting the amount of a nutrient required for growth but not for copolymer accumulation, the residence time of the aqueous medium in the vessel is made sufficiently long so as to allow exhaustion of the limiting nutrient, and for copolymer accumulation to occur.

In either a single or multistage process, or in batch or 7 B 35544 semi continuous or continuous process the HV component may be present as the sole source of carbon present in the substrate during all, or part of, the copolymer accumulation stage, or may be in admixture with other assimilable carbon sources.

The concentration of the HV component in the aqueous medium depends on a number of factors, e.g. whether the process is batch or continuous, the percentage copolymer desired, the percentage of HV monomer units in the copolymer desired. Because the bacterium used is capable of synthesising and accumulating copolymer at high conversion efficiencies, the concentration of •Y the HV component in the medium to, and hence medium from, the process is relatively low. Generally, the concentration of the HV component at the point of harvest of the bacterium is preferably between 0.1 and 25, and particularly between 5 and 10 g.1 15 The HV component may be propanol, propionic acid, or a salt, ester, anhydride, amide, or halide thereof.

Mixtures of compounds suitable for use as HV components may be used.

It is believed that the high conversion of HV component 20 to HV monomer units is made possible because the bacterium cultivated is no longer able to metabolise the HV component to acetyl CoA to a substantial extent.

Although we do not wish to be bound by the following theory, it is thought that the metabolic pathway leading to copolymers comprising HB monomer units and HV monomer units is as follows, in which CoA.SH is unesterified Coenzyme A,

CH

3 .CO.S.CoA is the acetyl thioester of Coenzyme A and is more commonly termed acetyl CoA, NADP is nicotinamide adenine dinucleotide phosphate in the oxidised state, and

NADPH

2 is reduced NADP.

It is believed that, in the biosynthesis of PHB by a micro-organism, the first step is the synthesis of acetyl CoA.

This can be formed for example, from CoA and acetate, or by the 8 B 35544 decarboxylation of pyruvate, which is the product of the glycolysis of carbohydrates, or which can be formed by decarhoxylation. of oxaloacetate, the latter being a member of the tricarboxylic acid (TCA) cycle, otherwise known as the Krebbs cycle.

Thus with acetate as the source of acetyl CoA, the PHB is produced by a metabolic pathway involving the reactions: 1. CH 3 .CO.O CoA.SH thiokinase CH 3 .CO.S.CoA OH 2. 2CH 3 .CO.S.CoA B ketothiolase GH 3

*CO.CH

2 .GO.S.CoA CoA.SH 3. GH 3

.GO.GH

2 *CO.S.CoA reductase CH 3

.CHOH.GH

2 .CO.S.CoA o NADPH 2

NADF

a 4. CH 3 .CHOH.C11 2 .CO.S.CoA polymerase- O.CH(CH 3

).GH

2 .CO CoA.SH 15 wherein

H

3

,GO.CH

2 .CO.S.CoA is acetoacetyl CoA,

CH

3

,CHOH.CH

2 .CO.S.CoA is 3 hydroxybutyryl CoA and

O.CH(CH

3

).GH

2 *GO Is a repeat unit in the polymer.

Thus reaction 4 adds O.GH(CH 3

).GH

2 *CO -to a growing So 20 polymer chain.

~:.Because of a lack of specificity of the enzymes involved, the correspording pathway with, for example propionic acid, is thought to be: @00990 Ia. CH 3

.CH

2 .C -c CoA.SH thiokinase- CH 3

.CH

2 .CO.S.GoA

OH-

2a. CH 3

,CH

2 ,CO.S.CoA B ketothiolase- ~CH 3

.CH

2

.GO.CH

2 .CO.S.CoA

CH

3 ,CO.S.GoA CoA.SH 3a. NADPH 2 reductase--> NADP

C

3 .C1 2

CO.CH

2 .CO.S.CoA 0H 3

,CH

2

.CHOH.CH

2 .CO.S.CoA 4a. CH 3

.CH

2

.CRH.GH

2 .CO.S.GoA polymerase--'-O.CH(C 2

H

5 ).11 2 .c0 CoA.SH wherein

CH

3

*CH

2 .GO.S.CoA is propionyl GoA,

CH

3

.GH

2 .CO.G11 2 .CO.SoCoA is 3 ketovaleryl CoA,

CH

3

-CH

2 oCHOH.CH 2 -CO-S.CoA is 3 hydroxyvaleryl CoA and 9 B 35544

O.CH(C

2 H5).CH2.CO is a repeat unit in the polymer.

Thus reaction 4 a adds O.CH(C 2

H

5

).CH

2 .CO to a growing polymer chain.

As hereinbefore postulated one of the intermediates in the synthesis of an HB monomer unit is itself an intermediate in the synthesis of an HV, it is therefore preferred that the substrate comprises not only an HV component but also a carbon source metabolisable to the required HB monomer intermediate, i.e.

an HB component. Thus by controlling the relative amounts in the substrate of components for HB and HV synthesis it is possible to obtain copolymers containing varying proportions of HB and HV monomer units.

A bacterium suitably adapted for use in the process of the present invention may be produced by the mutation of a PHB g* 15 accumulating strain of Alcaligenes eutrophus, and by screening and selecting of the resultant mutants.

Accordingly, we further provide a strain, in particular as a pure culture, of Alcaligenes eutrophus designated NCIMB 40124, and mutants and variants derived therefrom.

20 The strain Alcaligenes eutrophus NCIMB 40124 was deposited at the National Collections of Industrial and Marine Bacteria Ltd. (NCIMB), PO Box 31, 135 Abbey Road, Aberdeen AB9 8DG, United Kingdom on the 24 March 1989, under the terms and conditions of the Budapest Treaty.

The strain Alcaligenes eutrophus NCIMB 40124, and useful mutants and variants derived therefrom, may be characterised by the following taxonomic description. The strain, and mutants and variants derived therefrom are able to produce and accumulate PHB in a manner similar to that of the parent strain NCIB 12080, produce and accumulate copolymers containing HB and HV monomer units at high HV component to HV monomer conversion efficiencies, grow on a substrate consisting of acetate, but show no grow on a substrate consising of propionate. The combination of these growth, no growth, and polymer accumulation characteristics distinguish the new strains of Alcaligenes eutrophus from existing B 35544 strains of Alcaligenes eutrophus. The evaluation of the growth/no growth characteristics, mentioned above, were conducted under non growth limiting conditions, on substrate having a carbon content which was provided essentially by the material under test, i.e.

acetate or propionate.

Description of Alcaligenes eutrophus NCIMB 40124.

Morphology Gram negative motile rods of approximate size 0.8 ym x pm.

Evidence of intra cellular granules.

No spore formation.

Under a phase contrast microscope occasional subpolar flagella are noted.

Colonial morphology (Lab 8 Nutrient Agar) the organism 15 is in the form of round, regular, opaque, smooth, white convex colonies. After 3 days the diameter was about 2 mm.

A pale brown pigmentation developed with increasing age.

Temperature 20 At 5 0 C no growth.

At 37 0 C growth.

At 45 0 C no growth.

Characteristics Catalase Kovacs Oxidase 0-F Glucose very weakly oxidative Pyocyanin Fluorescence L-Arginine CSU Betaine CSU Glucose CSU Lactate CSU Acetate CSU CSU Arabinose Meso-inositol 11 B 35544 Xylose Gas Glucose

ONPG

Arginine Moller Lysine Moller Ornithine Moller

NO

3 to NO 2

NO

3 to N 2 at 37 0

C

DNA ase Gel stab.

Gel plate Casein Starch Lecithin egg 15 Lipase egg

NH

3 weakly positive Indole

H

2

S

Tween 80 20 Urease No growth exhibited on methanol at 5 or 14 days.

No growth exhibited on propan-1-ol at 5 or 14 days.

Growth exhibited on acetate at 3 days.

Resistant to penicillin G and stretomycin.

Sensitive to chloramphenicol, tetracycline, polymyxin B and novobiocin (weakly).

Strains of Alcaligenes eutrophus in accordance with the present invention may be produced in a variety of ways, for example, transposon mutagenesis including excision of inserted transposons which are able to cause deletions, chemical mutagenesis using mutagens such as ethane methane sulphonate and mutations caused by invitro manipulation and subsequent recombination.

Strain Alcaligenes eutrophus NCIMB 40124 was prepared in the following manner.

12 B 35544 The parent culture was Alcaligenes eutrophus NCIB 12080, available from the National Collection of Industrial and Marine Bacteria Ltd under the terms and conditions of the Budapest Treaty.

The parent culture was grown in mineral salts medium, plus glucose at to an optical density of 0.9, as measured at 600nm. A sample (10 mis) of the culture, as grown, was transferred to a 9 cm glass petri dish, and then irradiated with UV light at a dose level sufficient to achieve a kill of 99.9%.

The irradiated culture was transferred to a flask containing mineral salts medium, plus glucose at and o incubated, at 30 0 C, in the dark for about 16 hours.

10 mis of the incubated culture were then transferred to a flask containing mineral salts medium, plus sodium propionate at 15 0.075% and D-cycloserine at 800 pg.ml The contents of the flask were then incubated, at 30 0 C, for about 16 hours.

The culture was then centrifuged, and the resulting pellet resuspended in sterile distilled water.

Serial dilutions were made from the suspension and 20 0.1 ml aliquots plated from the dilutions onto mineral salts agar containing glucose at The plates were then incubated and the resulting colonies were replicated plated onto mineral salts agar, containing propionate at 0.075%.

Colonies were identified that were able to grow on the 0 S glucose agar plates but not the propionate agar plates. These S*0 colonies were selected for further investigation.

The selected colonies of putative mutants were screened for their ability to grow using glucose, or acetate, as a carbon source; their inability to grow on propionate; and their ability to produce and accumulate copolymer, comprising HB monomer and HV monomer units, when supplied with glucose and propionate under nitrogen limited conditions.

One strain produced according to the hereinbefore described procedure is Alcaligenes eutrophus NCIMB 40124.

The process of the present invention is illustrated by 13 B 35544 the following examples.

EXAMPLE 1 An aqueous medium containing the following, expressed as and having a pB of about 7 (controlled by ammonia addition) was prepared.

MgSO 4 .7H 2 0 2.2

K

2 S0 4 Na 2

SO

4 0.18 FeSO 4 .7H 2 0 0.18 Glucose 13.0 Trace elements 3.0 (m]s) S" Phosphoric Acid 6.5 (mls of 1.1 M) A fermenter containing 31 of the above medium was inoculated with a starter culture of Alcaligenes eutrophus NCIMB 15 40124. The inoculated medium was incubated, at 30 0 C, for 24 hours a ,e until the phosphate content of the medium became limiting.

a a Glucose, and propionic acid were chen fed to the fermenter at rates of 10 g.hr-1, and 3.3 g.hr-1 respectively, for a further 48 hours.

20 The cells containing the copolymer were harvested, freeze dried, and analysed for polymer content and composition.

0 1 EXAMPLE 2 Example 1 was repeated, except that the flow rates of the glucose and the propionic acid were 6.4 g.hr and 0.7 -1 g.hr respectively.

COMPARATIVE EXAMPLE 3 Example 1 was repeated, except strain Alcaligenes eutrophus NCIB 12080, was used instead of strain Alcaligenes eutrophus NCIMB 40124.

COMPARATIVE EXAMPLE 4 Example 2 was repeated, except strain Alcaligenes eutrophus NC1B 12080, was used instead of strain Alcaligenes eutrophus NCIMB 40124.

The results of Examples 1 to 4 were as folloas: B 35544 I Example I% HV Component I Conversion I I of I In Feed E n Copolymer I HV Component I 11 33 1 29 I88 2 11 U 7 64 C3 33 10 I I C4 I11 I5 It can thus be seen that the process of the present invention, employing a bacterium according to the invention, can give rise to substantial increase in the conversion efficiency of an 1W component into HV monomer units.

we I C CO.

9.

3 *d

C

CC

Ci

I.

.8 CCC

AC

9 9 CC CO.

B

CCC 4

CCBC

C

CC C

C'

4*

CCI

PA/EJN/JWR/MP

22 November 1990/P15A

Claims

1. A microbiological process for the production of copolymers comprising HB and HV monomer units using a PHB accumulating bacterium having substantially no major metabolic pathway for the conversion of HV component to HB monomer units and which is not capable of significant growth when cultivated under otherwise non growth limiting conditions on a substrate consisting essentially of an HV component, which process comprises cultivating the bacterium in an aqueous medium in which the substrate comprises a water soluble assimilable carbon containing HV component and a water soluble assimilable carbon containing HB component, at a desired weight of dry cells per litre of medium under growth limitation conditions conducive to the bacterium synthesising and accumulating copolymer, and thereafter harvesting the copolymer containing bacterium.

2. A microbiological process for the production of copolymers comprising HB and HV monomer units using a PHB accumulating bacterium from which a mFjor metabolic pathway for the conversion of HV component to HB monomer units has been substantially eliminated and which is not capable of significant growth when cultivated under otherwise ion growth limiting conditions on a substrate consisting essentially of an HV component, which process comprises cultivating the bacterium in an aqueous medium in which the substrate comprises a water soluble assimilable carbon containing HV component and a water soluble assimilable carbon containing HB component, at a desired weight of dry cellu per litre of medium under growth limitation conditions conducive to the bacterium synthesising and accumulating copolymer, and thereafter harvesting the copolymer containing bacterium.

3. A process as claimed in claim 1 or 2 wherein the 3: 5 bacterium is capable of converting more than 45% of the HV component present in the substrate into HV monomer units. 000

4. A process as claimed in any one of claims I to 3 wherein the concentration of the HV component in the aqueous medium is V-x 16 controlled in order to achieve a desired percentage of HV monomer units in the copolymer.

A process as claimed in any one of claims 1 to 4 wherein the concentration of the HV component in the medium associated with the harvested bacterium is between 0.1 and 25 g.1l

6. A process as claimed in any one of zlaims 1 to 5 wherein the HV component is propanol, propionic acid, or an assimilable derivative thereof.

7, A process as claimed in any one of claims 1 to 6 wherein the cultivation of the bacterium is conducted so that the dry weight of the copolymer containing cells is at least 30 g.l-

8. A process as claimed in any one of claims 1 to 7 wherein the cultivation of the bacterium comprises a two stage process, such that in a first stage the bacterium is grown to the desired dry weight per litre, under non growth limiting conditions on a readily metabolisable substrate and in a second stage the substrate is at least in part the HV component, and at least one nutrient required for growth is limited, such that the growth limiting conditions exist.

9. A process as claimed in any one of claims 1 to 8 wherein the growth limitation conditions are achieved by limiting the amount of assimilable nitrogen and/or phosphorus availa'.e.

A process as claimed in claim 9 wherein the amount of S.*0 assimilable nitrogen available is about 10 to 15% by weight of the desired weight of cells less the weight of the accumulated copolymer.

11. Alcaligenes eutrophus strain NCIMB 40124, or mutan.ts or variants thereof wherein the mutants or variants are not capable Sof significant growth when cultivated under non growth limiting conditions on a substrate having a water soluble carbon content, "e and the water soluble carbon content is provided essentially by San HV component. D'^ 17

12. A process for producing a PHB accumulating bacterium whicn is capable of producing copolymers comprising HB and HV units from a substrate comprising HB and HV components which has no major metabolic pathway for the conversion of HV component to HB monomer units and which is not capable of significant growth when cultivated under otherwise non growth limiting conditions on a substrate consisting essentially of an HV component which process comprises substantially eliminating a major metabolic pathway for the conversion of HV component to HB monomer units from a PHB accumulating bacterium.

13. A process, as claimed in claim 1, substantially as hereinbefore described with reference to any one of the examples. DATED: 22 March 1993 PHILLIPS ORMONDE FITZPATRICK Attorneys for: 04c7dt P IMPERIAL CHEMICAL INDUSTRIES PLC 2464N DO go *S